Static Electricity Principles of Physics

Charge is the ability to attract or repel Q (large charges)q (small charges) Units: coulombs (C) Types of charge: positive or negative neutral → no charge

Charged particles: Electron – around nucleus Charge = -1 elementary charge (-1e) Proton – in nucleus Charge = +1 elementary charge (+1e)

Amount of charge a particle has is proportional to the number of excess electrons or protons Q = NeQ = charge (C) = q N = number of excess charges e = elementary charge = charge of a proton when + = charge of an electron when -

Example: A charged sphere has an excess of 15 protons. What is the charge of the sphere? Q = Ne = +15e

Like charges REPEL Unlike charges ATTRACT

A force exists between all charged bodies  When the charges are like the force causes them to move away  When the charges are unlike the force causes them to toward each other  According to Newton’s 3 rd law, if one charged body acts on another, the other acts back on it with the same force +Q -q +q F1F1 F1F1 F2F2 F2F2

A force exists between all charged bodies  Inverse relationship between force and distance  Force increases when distance decreases  Force decreases when distance increases  Direct relationship between force and charge  Force increases when charge increases  Force decreases when charge decreases

Conductors: metals  lots of loosely connected, easily moved electrons Insulators: plastic, ceramics  Tightly bound electrons Semiconductors: Silicon, Germanium  Semi-tight electrons – more movement at high temps  Conductivity affected by doping (adding materials that help control conduction)

Source (donator) or sink (acceptor) of an infinite amount of charge without significantly changing its own charge Examples: 1. Earth 2. You

Methods 1. Inducing a charge (Induction)  Neutral objects can act charged when placed near a charged object 2. Charge by Conduction  Charging by touch 3. Permanently charge by induction  Charging by touching to ground

 When a negatively charged object is brought near a neutral object, electrons move away from it  The object attract because the unlike charges are near  When a positively charge object is brought near a neutral object, electrons in the neutral object move toward it  The objects attract because unlike charges are near

Balloon (rubbed over hair) Wall (Neutral)

The charges in the wall separate

 Charge transfers directly from one object to another  Results in equal charge on all objects  Charges distribute evenly between objects

Example: A sphere with a charge of -4e touches a sphere with a charge of -6e. What is their charge after they separate again? Together they have:After they separate they -6e + -4e = -10eeach have: -10e/2 = -5e

Example: A sphere with a charge of -4e touches a sphere with a charge of +8e. What is their charge after they separate again? Together they have:After they separate they +8e + -4e = +4eeach have: +4e/2 = +2e

 Charging by touching to ground

 Transfer of opposite charge, but same amount Example: If charged object has a charge of +24e, then object charged by induction will have -24e.